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Handbook of Clinical Neurology 2019Of the principal sensory systems (vision, olfaction, taste, hearing, and balance), olfaction is one of the oldest. This ubiquitous system has both peripheral and central... (Review)
Review
Of the principal sensory systems (vision, olfaction, taste, hearing, and balance), olfaction is one of the oldest. This ubiquitous system has both peripheral and central subdivisions. The peripheral subdivision is comprised of the olfactory epithelium and nerve fascicles, whereas the central subdivision is made up of the olfactory bulb and its central connections. Humans lack the "accessory olfactory system" of many other mammals, exhibiting only a nonfunctioning vestige of its peripheral element, the vomeronasal organ. Compared to most mammals, major elements of the human olfactory system are reduced; for example, humans have fewer turbinates than many mammals, and their olfactory epithelia are found only on one or two of these structures and their adjacent surfaces. Nonetheless, humans retain a full complement of functional cellular elements including a regenerating population of olfactory sensory neurons. These neurons extend long ciliary processes into the mucus that form a mat of cilia on which the odorant receptors are located. The olfactory sensory neurons send their axons directly to synapse within the olfactory bulb. Mitral and tufted cells then relay impulses from the bulb to other brain regions. This chapter describes the general anatomy and microanatomy of the olfactory system.
Topics: Animals; Axons; Brain; Humans; Nerve Tissue; Neurons; Olfactory Bulb; Smell
PubMed: 31604545
DOI: 10.1016/B978-0-444-63855-7.00002-2 -
Life Sciences Feb 2018Neurological diseases are becoming increasingly prominent worldwide due to rapidly aging populations, which greatly contributes to increasing healthcare costs. The... (Review)
Review
Neurological diseases are becoming increasingly prominent worldwide due to rapidly aging populations, which greatly contributes to increasing healthcare costs. The development of neuroprotective drugs has so far proven exceptionally difficult due to the blood-brain barrier. One novel approach to address this challenge is to administer drugs intranasally to noninvasively bypass the blood-brain barrier. The intranasal route can thus transport drugs directly to the brain from the nasal cavity along the olfactory and trigeminal nerves. The purpose of this review is to describe the details of this mechanism to better direct future research. The intranasal route is composed of two pathways, one being intracellular while the other being extracellular. The intracellular pathway begins with endocytosis by olfactory sensory cells, followed by axonal transport to their synaptic clefts in the olfactory bulb where the drug is exocytosed. This transynaptic process is repeated by olfactory neurons, thereby distributing the drug to other brain regions. In the extracellular mechanism, drugs are transported directly into the cerebral spinal fluid by first passing through the paracellular space across the nasal epithelium, then through the perineural space to the subarachnoid space of the brain. With a growing body of evidence and trials in both rodent and human models, this is an exciting area for research as therapeutics come to market.
Topics: Administration, Intranasal; Animals; Blood-Brain Barrier; Brain; Drug Delivery Systems; Humans; Nasal Cavity; Nervous System Diseases
PubMed: 29277310
DOI: 10.1016/j.lfs.2017.12.025 -
Cell Jan 2020Molecular interactions at the cellular interface mediate organized assembly of single cells into tissues and, thus, govern the development and physiology of...
Molecular interactions at the cellular interface mediate organized assembly of single cells into tissues and, thus, govern the development and physiology of multicellular organisms. Here, we developed a cell-type-specific, spatiotemporally resolved approach to profile cell-surface proteomes in intact tissues. Quantitative profiling of cell-surface proteomes of Drosophila olfactory projection neurons (PNs) in pupae and adults revealed global downregulation of wiring molecules and upregulation of synaptic molecules in the transition from developing to mature PNs. A proteome-instructed in vivo screen identified 20 cell-surface molecules regulating neural circuit assembly, many of which belong to evolutionarily conserved protein families not previously linked to neural development. Genetic analysis further revealed that the lipoprotein receptor LRP1 cell-autonomously controls PN dendrite targeting, contributing to the formation of a precise olfactory map. These findings highlight the power of temporally resolved in situ cell-surface proteomic profiling in discovering regulators of brain wiring.
Topics: Animals; Axons; Brain; Dendrites; Drosophila Proteins; Drosophila melanogaster; Gene Expression Profiling; Gene Expression Regulation, Developmental; Membrane Proteins; Neurogenesis; Olfactory Nerve; Olfactory Pathways; Olfactory Receptor Neurons; Proteomics; Receptors, Lipoprotein; Smell
PubMed: 31955847
DOI: 10.1016/j.cell.2019.12.029 -
Seminars in Ultrasound, CT, and MR Oct 2022The human sense of smell is the unique sense through which the olfactory system can identify aromatic molecules within the air and provide a taste sensation. Still, also...
The human sense of smell is the unique sense through which the olfactory system can identify aromatic molecules within the air and provide a taste sensation. Still, also it plays an essential role in several other functions, warning about environmental safety and even impacts our emotional lives. Recently, olfactory impairment has become an issue of interest due to the COVID-19 pandemic. The dysfunction may vary from only reduced smell detection (hyposmia) to complete loss of it (anosmia) but also includes changes in the normal perception of odors (parosmia). Computed tomography and magnetic imaging resonance are the modalities of choice to evaluate the olfactory pathways. Computed tomography is the initial imaging modality for olfactory disturbances, allowing recognition of sinonasal pathologies, inflammatory processes, or bone-related tumors. Magnetic imaging resonance with dedicated protocols for olfactory disorders enables a detailed assessment of the sinonasal compartment and the anterior cranial fossa. Provides a better depiction of olfactory bulb volume, morphology and signal intensity, as well the status of signal intensity of the central olfactory projection areas. Several diseases can affect the olfactory nerve, such as congenital disorders, trauma, inflammatory or infectious diseases, neoplasms, and even post-operative involvement. This article aims to review the normal anatomy of the olfactory nerve pathway and highlight the spectrum of conditions that most commonly affect it.
Topics: COVID-19; Humans; Olfaction Disorders; Olfactory Bulb; Olfactory Nerve; Pandemics
PubMed: 36116849
DOI: 10.1053/j.sult.2022.04.001 -
Auris, Nasus, Larynx Apr 2016Impairment of smell may occur following injury to any portion of the olfactory tract, from nasal cavity to brain. A thorough understanding of the anatomy and... (Review)
Review
Impairment of smell may occur following injury to any portion of the olfactory tract, from nasal cavity to brain. A thorough understanding of the anatomy and pathophysiology combined with comprehensively obtained history, physical exam, olfactory testing, and neuroimaging may help to identify the mechanism of dysfunction and suggest possible treatments. Although most olfactory deficits are neuronal mediated and therefore currently unable to be corrected, promising technology may provide novel treatment options for those most affected. Until that day, patient counseling with compensatory strategies and reassurance is essential for the maintenance of safety and QoL in this unique and challenging patient population.
Topics: Activities of Daily Living; Brain Contusion; Brain Injuries, Traumatic; Cerebral Cortex; Facial Bones; Facial Injuries; Fractures, Bone; Humans; Magnetic Resonance Imaging; Nose; Olfaction Disorders; Olfactory Nerve Injuries; Paranasal Sinuses; Positron-Emission Tomography; Quality of Life; Tomography, Emission-Computed, Single-Photon
PubMed: 26441369
DOI: 10.1016/j.anl.2015.08.006